Every request on mongos and mongod that has client metadata will update the API version metrics tracking stats. The stats are stored in a map of maps of std::strings to a Date_t. Looking up from this map requires the client's application name as a std::string, which requires converting a StringData into a std::string (e.g. on mongos). We should be able to skip this by using a StringMap which stores std::string keys but can be looked up in by StringData.